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NASA Technical Memorandum 100761 

I

The Pioneer Venus Orbiter: 

11 Years of Data 

A Laboratory for Atmospheres Seminar Talk 

W. T. Kasprzak 

MAY 1990

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11 YEARS OF DATA. A LABORATORY FOR 

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NASA
NASA Technical Memorandum 100761 

The Pioneer Venus Orbiter: 

11 Years of Data 

A Laboratory for Atmospheres Seminar Talk 

W. T. Kasprzak 

Goddard Space Flight Center 

Greenbelt, Maryland 

NASA 

National Aeronautics and 

Space Administration 

Goddard Space Flight Center 

Greenbelt, MD

ORIGINAL CONTAINS

COLOR ILLUSTRATIONS

1990
PREFACE 

The contents of this document were originally presented 

as a Laboratory for Atmospheres seminar talk entitled "TEN 

YEARS OF VENUS DATA" on January 23, 1990. 

j

PRECEDING PAGE BLANK NOT FILMED
CONTENTS 

1. INTRODUCTION...................................1 

2. GEOLOGY........................................17 

3. ATMOSPHERE ..................................... 27 

4. IONOSPHERE/SOLAR WIND INTERACTION..............58 

5. SOLAR ACTIVITY EFFECTS.........................64 

6. SUMMARY ........................................ 77 

7. REFERENCES .....................................78 

/

V

PRECEDING PAGE BLANK NOT FILMED
Pioneer 12 takes a licking but craft keeps a ticking"

(Associated Press, Dec. 6, 1988, D. M. Kunten) 

The ancient astronomers knew of Venus. For example, the 

Mayans of central Mexico did not recognize Venus as a planet. 

They called it the evening star when seen in the western sky 

after sunset and the morning star when seen in the eastern 

sky before sunrise. The Mayans, however, knew the synodic 

period was 583.9 days. The Greeks first recognized the 

morning and evening star as a single object calling it 

Cytherea after the island sacred to Aphrodite (the goddess of 

love). The Romans called it Venus. Venus is the brightest 

object in the night sky after the moon. Its astronomical 

symbol is the hand mirror symbolizing its reflected 

brilliance. Modern data on Venus is shown in Table 1.1. 

On December 4, 1978 a satellite was inserted into orbit 

around Venus in order to determine the salient features of 

the planet, it atmosphere/ionosphere, and interaction with 

the solar wind (ref. 4). The 10th anniversary of the Pioneer 

Venus Orbiter was celebrated at Ames Research Center with a 

symposium describing the main contributions of the Orbiter to 

the general understanding of Venus (ref. 1). The Orbiter has 

operated successfully the past 11 years gathering remote and 

in situ data over most of the solar cycle, and will continue 

operation until reentry into the atmosphere in 1992. Although 

Venus and Earth are often called twin planets, they are only 

superficially similar. Possessing no obvious evidence of 

plate tectonics, lacking water and an intrinsic magnetic 

field, and having a hot dense carbon dioxide atmosphere with 

sulfuric acid clouds makes Venus a unique object of study by 

the Orbiter's instruments.
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The quotation at the beginning of the introduction 

refers to the fate of the Orbiter. Since Venus is closer to 

the Sun than the Earth, the satellite is subject to more 

heating than it would at earth. The lack of an intrinsic 

magnetic field does not protect the satellite from the 

effects of solar flares. As of this date the Orbiter 

infrared spectrometer has failed and the magnetometer has 

partially failed; the solar panel power output is gradually 

diminishing with time; and the hydrazine fuel used for orbit 

maneuvers is almost gone. In 1992 the satellite will reenter 

the atmosphere and burnup. 

The mission began as a study at Goddard Space Flight 

Center (ref. 2a). It soon evolved into a single orbiter and a 

bus carrying 4 lower atmosphere probes with project 

management at Ames Research Center. The mission was to be low 

cost (Table 1.2) (ref. if) with the same basic spacecraft 

design being used for both the orbiter and bus (the beginning 

of the "universal bus" concept). The Orbiter has produced 

quite a few data bits. Much of that data have been analyzed 

and reported in the literature (ref. 3). 

The goals of the lower atmosphere probes and the orbiter 

are summarized in Table 1.3. Prior to 1962, the first 

spacecraft visit to Venus, quite a bit was known about the 

planet and there was considerable speculation about what lay 

underneath the obscuring clouds (Table 1.4) (ref. 281). 

Today, after many spacecraft visits and remote Earth 

observations considerably more is known. Venus has a hot, 

dense carbon dioxide atmosphere with high altitude sulfuric 

acid clouds. There are no oceans on Venus and it has been at 

least 4 billion years since there may have been enough water 

to have formed one. The lack of an intrinsic magnetic field 

has two implications: a) the solar wind interacts directly 

with the ionosphere rather than a magnetic field as in the 

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Table 1.4. Venus Before the First Spacecraft Visit and Now (Ref. 28i) 

FACTS KNOWN ABOUT VENUS PRIOR TO 1962 (FIRST SPACECRAFT VISIT): 

1) Rich CO atmosphere 

2) Opaque clouds obscure surface 

3) Substantial flux at radio wavelengths 

4) Lower atmosphere hot and dense 

5) Surface smooth compared to Earth's 

SPECULATION ABOUT VENUS: 

1) Moist, swampy, teeming with life OR 

2) Warm with carbonic acid ocean (i.e. seizer water) OR 

3) Cool, Earth—like, surface water, dense ionosphere OR 

4) Warm, massive clouds of water, continual rain with lightning OR 

5) Cold at pole with 10—km icecaps, hot at equator with water

above boiling point OR 

6) Hot, dusty, dry, windy, global desert OR 

7) Very hot, cloudy, molten lead and zinc puddles at equator, 

seas of bromine, butyric acid and phenol at poles 

NOW:

1) Mainly CO atmosphere (96.5% CO 2, 3.5% N2); surface 

pressure 92 atmospheres; sulfuric acid clouds (50 to 70 km) 

2) Virtually no water ( lOOppm in atmosphere; no oceans) 

3) Rocky surface at very high temperature (735 Kelvin) 

4) Ionosphere comparable to Earth's, no intrinsic magnetic field 

5) Plateaus and mountains on Venus as high or higher than on Earth 

but lowlands only one—fifth the greatest depth of those on Earth 

N. 
case of the Earth (ref. 7); b) there are no radiation belts 

although Venus does possess atomic oxygen aurora (refs. 5,6). 

The surface of Venus is generally not any higher than the 

Earth but it possesses no lowlands equivalent to the Earth's 

ocean basins. 

Since 1962, 22 American and Soviet spacecraft have 

visited Venus as orbiters, fly-bys, lower atmosphere probes 

and balloons floating at the cloud tops (Table 1.5). The 

U.S. Magellan Mission will arrive at Venus in August, 1990. 

It carries a single instrument, a high resolution radar 

mapper. The Pioneer Venus Mission is summarized in Table 1.6 

(ref. 2a). Like all projects Pioneer Venus began with a 

series of questions about Venus (Table 1.7) and then asked 

what instruments, probes, and spacecraft types could help to 

answer those questions. Reference la lists the experiments, 

principal investigators, guest investigators and 

interdisciplinary scientists for the Orbiter. 

The Orbiter is shown in Figure 1.1 (ref. 2). The 

diameter is 2.54 m, it is 1.2 m tall, weighs 582 kg with a 

science payload of 43 kg. The silicon solar cells are shown 

as a black band around the sides. The spacecraft maintains 

stability by spinning about an axis indicated by the 

telemetry antenna. There are 12 active experiments on board 

the spacecraft, three of which originated at Goddard Space 

Flight Center (Electron Temperature Probe, Ion Mass 

Spectrometer and Neutral Mass Spectrometer). There are three 

passive experiments: a) radio occultation which uses the 

spacecraft antenna transmissions to deduce properties of the 

atmosphere and ionosphere; b) atmospheric drag which 

determines the atmospheric density at periapsis from changes 

in the orbital period; and o) gravimetrics which uses orbital 

perturbations to deduce surface mass concentrations. 

VA
Table 1.5. U.S. and Soviet Spacecraft Missions to Venus 

SPACECRAFT LAUNCH COMMENT 

Mariner 2 27-Aug-62 Fly-by 14-Dec-62 

Venera 3 16-Nov-65 Venus impact 01-Mar-66 

Venera 4 12-Jun-67 Soft atmospheric entry 18-Oct-67 

Mariner 5 14-Jun-67 Fly-by 19-Oct-67 

Venera 5 05-Jan-69 Soft atmospheric entry 16-May-69 

Venera 6 10-Jan-69 Soft atmospheric entry 17-May-69 

Venera 7 17-Aug-70 Soft surface landing 15-Dec-70 

Venera 8 27-Mar-72 Soft surface landing 22-Jul-72 

Mariner 10 03-Nov-73 In solar orbit: Venus flu-by 

05-Feb-74; Mercury fly-by 29-Mar-74, 

in Sep-74 and Mar-75 

Venera 9 08-Jun-75 Orbiter and surface lander 22-Oct-75 

Venera 10 14-Jun-75 Orbiter and surface lander 25-Oct-75 

Pioneer 20-May-78 Orbiter: 04-Dec-78 

Venus 1 

Pioneer 08-Aug-78 Multiprobes enter atmosphere 

Venus 2 09-Dec-78 week after arrival of 

orbiter 

Venera 11 09-Sep-78 Fly-by; soft lander, dayside 

25-Dec-78 

Venera 12 14-Sep-78 Fly-by; soft lander, dayside 

21-Dec-78 

Venera 13 30-Oct-81 Soft lander 01-Mar-82 

Venera 14 04-Nov-81 Soft lander 05-Mar-82 

Venera 15 02-Jun-83 Radar mapper 10-Oct-83 

Vener-a 16 07-Jun-83 Radar mapper 14-Oct-83 

Venera 15-Dec-84 Balloon 11-Jun-85 

Halley 1 Halley's comet 06-Mar-86 

(VEGA 1) 

Venera 21-Dec-84 Balloon 14-Jun-85 

Halley 2 Halley's comet 09-Mar-86 

(VEGA 2) 

Magellan 06-May-89 Radar mapper Aug-90 arrival 

Galileo 19-Oct-89 Fly-by 10-Feb-90; remote sensing 

Venera spacecraft are USSR spacecraft; the remainder are USA 

spacecraft. The best earth to Venus launch opportunities 

occur about every 19 months.

8 
Table 1.6. Pioneer Venus Mission, Its Instrument Types and Requirements (Ref. 2a) 

DATE MILESTONE 

1968 National Academy of Sciences recommends mission 

1974 Spacecraft and science payload selected 

1975 Start instrument design 

20-MAY-1976 Launch orbiter spacecraft 

08-AUG-1978 Launch multi-probe spacecraft 

04-DEC-1978 Orbiter encounters Venus 

09-DEC-1978 Multi-probe encounters Venus 

Today Orbiter still functioning; periapsis at 2000 km 

1992 Re-enter atmosphere and burn-up 

INVESTIGATION TYPE 

Atmospheric composition! 

Structure 

Clouds 

Thermal balance 

Dynamics/Turbulence 

Solar wind/ionosphere 

Surface/interior 

Astronomy

INSTRUMENT TYPES 

Mass spectrometer 

Ultra-violet Spectrometer 

Gas chromatograph 

Accelerometers and 

temperature probes 

Nephelometer 

Cloud particle spectrometer 

Phot opolarimeter 

Infrared and solar flux 

radiometer 

Multi-probe tracking 

Radio occultation 

Magnetometer 

Electric field detector 

Ion mass spectrometer 

Electron density/temperature 

probe 

Plasma analyzer(s) 

Radio occultation 

Radar mapper 

Orbital celestial mechanics 

Gamma-ray burst detector 

INSTRUMENT REQUIREMENTS 

Low power (solar cells,batteries) 

Low weight (launch vehicle,propellant limitations) 

Small size C

SI

) 

Adaptable to a wide range of measurement conditions 

(exploring new territory) 

Operate UNATTENDED for years (no on-site repair) 

Survive Environment (temperature, radiation ,vacuum) 

Survive earth launch (vibration)

Le
Table 1.7. Questions for the Pioneer Venus Mission (Ref. 2a) 

1. Cloud layers: What is their number and where are they 

located? Do they vary over the planet? 

2. Cloud forms: Are they layered, turbulent, or merely hazes? 

3. Cloud physics: Are the clouds opaque? What are the sizes 

of the cloud particles? How many particles are there per 

cubic centimeter? 

4. Cloud composition: What is the chemical composition of 

the clouds? Is it different in the different layers? 

5. Solar heating: Where is the solar radiation deposited 

within the atmosphere? 

6. Deep circulation: What is the nature of the wind in the 

lower regions of the atmosphere? Is there any measurable 

wind close to the surface? 

7. Deep driving forces: What are the horizontal differences 

in temperature in the deep atmosphere? 

8. Driving force for the 4-day circulation: What are the 

horizontal temperature differences at the top layer of 

clouds that could cause the high winds there? 

9. Loss of water: Has water been lost from Venus? If so, how? 

10. Carbon dioxide stability: Why is molecular carbon dioxide 

stable in the upper atmosphere? 

11. Surface composition: What is the composition of the 

crustal rocks of Venus? 

12. Seismic activity: What is its level? 

13. Earth tides: Do tidal effects from Earth exist at Venus, 

and if so, how strong are they? 

14. Gravitational moments: What is the figure of the planet? 

What are the higher gravitational moments? 

15. Extent of the 4-day circulation: How does this 

circulation vary with latitude on Venus and depth in the 

atmosphere? 

16. Vertical temperature structure: Is there an isothermal 

region? Are there other departures from adiabaticity? 

What is the structure near the cloud tops? 

17. Ionospheric motions: Are these motions sufficient to 

transport ionization from the day to the night 

hemisphere? 

18. Turbulence: How much turbulence is there in the deep 

atmosphere of the planet? 

19. Ion chemistry: What is the chemistry of the ionosphere? 

20. Exospheric temperature: What is the temperature and does 

it vary over the planet? 

21. Topography: What features exist on the surface of the 

planet? How do they relate to thermal maps? 

22. Magnetic moment: Do the planet have internal magnetism? 

23. Bulk atmospheric composition: What are the major gases in 

the Venus atmosphere? How do they vary at different 

altitudes? 

24. Anemopause: How does the solar wind interact with the 

planet?

10
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Figure 1. 1. An artist's conception of the Orbiter in place around Venus (ref. 2). 

11

ORIGINAL PAGE 

COLOR PHOTOGRAPH
Figure 1.2 (refs. 2a,2b) shows the situation at the 

initial encounter with Venus. The Orbiter is in place around 

the planet and the lower atmosphere probes, having been 

released from the Bus, impact on the surface at the locations 

shown. The Bus, carrying an ion and neutral mass 

spectrometer, will burn up near the morning terminator. The 

orbit is nearly polar with an inclination of about 15 

degrees, has a nominal 24 hour period, with initial periapsis 

near 150 km and apoapsis near 66000 km. The position of the 

orbit in 1978-80, during initial encounter, and in 1992, 

during the final reentry phase, are shown in the bottom of 

figure 1.2. 

The evolution of the orbit's periapsis altitude is shown 

in Figure 1.3 (ref. 2b). For the first 600 orbits periapsis 

was maintained near 150 km by propulsion. In situ 

measurements of the atmosphere and main ionosphere were 

possible during this phase. After this period periapsis was 

allowed to drift upward to a maximum of 2300 km due solar 

gravitational perturbations and is now drifting downward due 

to the same perturbation. In 1992 the spacecraft will reenter 

the atmosphere and finally burn up. 

A comparison of Earth and Venus to scale is shown in 

Figure 1.4 (ref. 8a). The picture of Venus was taken in the 

ultraviolet to show the cloud structure. As can be seen in 

Table 1.1 Earth and Venus are very similar in radius, mass, 

density and gravitational acceleration. The sulfuric acid 

clouds rotate about the planet once every 4 days in a 

retrograde fashion (contrary to the direction of rotation of 

the Earth). This may not seem remarkable until it is 

realized that the planet takes 243 days to complete one 

rotation about its axis. The axis of Venus is almost 

perpendicular to its orbit plane and the orbital eccentricity 

is very small so that there are no seasons on Venus. 

13 

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Figure 1.2. The Orbiter in position, the bus has released its probes (top) (ref. 2a). The 

orbit as it appeared in 1978-80 and as it will appear in 1992 (bottom) (ref. 2b). 

14
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The upper limit on the magnetic moment in Table 1.1 is 

based on magnetometer data (ref. 9). The implication is that 

today Venus has no active internal dynamo. The requirements 

for a planetary dynamo (refs. 10,11) are: a) an electrically 

conducting fluid such as iron which is usually present in the 

core of planets and has a conductivity comparable to copper 

at high temperatures; and b) convective motion of the fluid 

(for example, a helical motion along the main direction of 

motion has been suggested for the Earth). The energy source 

can be: a) radioactive decay of potassium 40; b) settling of 

a denser iron phase through a less dense phase; or c) the 

latent heat of fusion when the core freezes out. Models (ref. 

11) of the Venus core suggest that it has a slightly higher 

core temperature and lower core pressure than the Earth and 

that this has prevented the core from freezing out. With not 

enough heat flux or planetary rotation to drive the 

convection, the core stratifies. No internal dynamo or 

external magnetic field develops. 

Earth and Venus differ internally as well as externally 

on the surface (ref. 17). Figure 2.1 shows the hypsographic 

graph of Venus derived from radar measurements; Earth is also 

shown (ref. 12,15). The percentage of area within a one 

kilometer altitude interval relative to a mean surface (sea 

level for the Earth and 6051.4 km for Venus) is plotted as a 

function of the altitude. Earth has a distinctly bimodal 

distribution reflecting the continents (about 35% of the area 

centered on zero) and the ocean basins (about 65% centered 

around -5 km). Venus is distinctly unimodal with 60% of the 

surface within a half kilometer of the mean surface. The 

continental regions of Venus are not generally higher than 

those of the Earth but a large fraction of Earth's oceans are 

5-6 km below sea level unlike Venus (ref. 28f). 

17
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Figure 2.2 (refs. 20,13) shows the typographic map for 

Venus. In the top panel, the highlands are indicated by 

hatched shading and represent areas higher than 2 km above 

the mean surface. Ishtar Terra is about the size of 

Australia. Maxwell Montes is the highest feature on Venus (11 

km), taller than Mount Everest, and looks like an ancient 

volcano. Aphrodite Terra is the size of Africa and possesses 

gigantic rift valleys comparable to those seen on Mars. 

Currently there is a controversy as to whether Aphrodite 

represents a spreading center like the mid-Atlantic ridge on 

Earth (refs. 1b,14). Beta Regio consists of 2 gigantic, cone 

shaped, shield volcanoes similar to those seen in Hawaii. It 

has been suggested that this feature is being supported by 

similar convective processes. The dotted areas in the top 

panel, the lowlands, represent surfaces that are below the 

mean surface level. The white areas are the rolling plains 

between the highlands and lowlands. Some features look like 

meteor impact craters and crater size counts imply the 

surface is between 500 million years to 1 billion years old 

(refs. 12). The existence of the highlands seems to imply' 

that there is little water in the rocks of Venus, at least 

compared to Earth standards, since water rich crustal rooks 

at the high temperature of Venus would tend to flow and the 

highlands would flatten out (ref. 18). The gravitational 

field closely matches the continental typography (ref. 16). 

Apparently significant relaxation has occurred similar to the 

old mountain ranges on Earth (ref. ib). The radar 

typography and surface roughness are very suggestive of 

basaltic lava flows of the effusive or b oozing" type rather 

than the more explosive type (ref. 25). 

Altimeter data for Venus derived from the radar mapper 

is shown in Figure 2.3 (refs. 8b,19); white is the highest 

altitude area and blue the lowest. Earth has been processed 

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to the same spatial resolution as is available from the radar 

mapper on Venus. Venus has no tell-tale ridges or rifts. 

There are no characteristic jigsaw patterns around the 

continents. There is a lack of mid-ocean ridges and 

subduction trenches where the sea floor slides beneath the 

continental plates. Plate tectonics, so dominant on earth, 

seems to play minor role, if any, on Venus. Models of the 

surface suggest the high surface temperature has led to the 

development of a thick basaltic crust that cannot be 

subducted (ref. 28f). The heat release appears to be through 

conduction, similar to the "hot spot" volcanoes on the Earth 

like the Hawaiian chain which are not associated with plate 

boundaries (refs. 16,21,42). 

Pictures of the surface of Venus have been taken by 

Soviet Venera spacecraft landing near Beta Regio (refs. 

24,25). X-ray fluorescence measurements confirm a basaltic 

composition of the surface (i.e. silicate minerals high in 

iron and magnesium) (refs. 15,16,22,23,28g). Figure 2.4 

(ref. 26) shows two surface pictures of Venus. The curvature 

in the picture is a result of the method used in taking the 

picture. The top panel shows the surface as it appears in 

natural light. The yellow color is due to incident light on 

Venus which has virtually all of the blue region of the 

spectrum scattered out by the atmosphere and clouds. The 

lower panel shows the "true" color of the surface as it would 

appear in white light with the atmosphere component removed. 

The surface of Mars is rust colored due to iron oxides; Venus 

might be expected to be similar in color. At 500 C dark red 

ferric minerals are red only in the infrared, black in the 

visible. The reflectance spectrum is consistent with 

basaltic minerals having a ferric component. The iron oxides 

could act as a sink for the oxygen associated with the 

assumed high abundance of water in the early days of Venus. 

In this scenario water is photodissociated into hydrogen 

23 

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(which escapes from the planet) and oxygen which combines 

with the surface minerals. The iron oxides are' also important 

in the geologic sulfur cycle.

24
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Figure 3.1 shows the temperature distribution and 

nomenclature for the atmosphere of Earth (ref. 27a) and Venus 

(ref. 28a). For Earth the boundary between the stratosphere 

and the mesosphere has a temperature maximum due to 

ultraviolet absorption by ozone. On Venus there is no 

detectable temperature maximum in this region and ozone is 

below detectable limits (Table 3.1) (ref. 27b,28b). There is 

no stratosphere on Venus. From bottom to top: the troposphere 

extends from the ground to the bottom of the cloud layer 

(about 50 km); the mesosphere extends from there to the point 

where the temperature increases; the thermosphere (or "hot" 

sphere) extends to the exobase; and the exosphere from the 

exobase upward. In the exosphere the density scale height is 

comparable to or greater than the mean free path and 

particles can execute ballistic trajectories from one part of 

the planet to another (ref. 27e). The dotted line is the cold 

night side thermosphere and exosphere (exospheric temperature 

near 100 ), colder than the underlying mesosphere, called 

the cryosphere (or "cold" sphere). The orbiter in situ 

measurements occur above 140 km in the exosphere. The 

mesosphere is where most of the ultraviolet absorption and 

chemical activity takes place. The chlorine chemistry keeps 

the ozone and molecular oxygen below detectable limits (ref. 

10). It is also responsible for maintaining the stability of 

carbon dioxide in the thermosphere and exosphere (ref. 27c). 

Chlorine also plays a role in the destruction of ozone in the 

Antarctic ozone hole (ref. lo) on Earth. The planetary cold 

trap (ref. 27a) for Earth is near the tropopause at 15 km, 

195 C. Below this level the water vapor content of the 

troposphere is variable but of the order of several percent. 

Above this level, in the stratosphere, it is about 5 ppm. The 

tropopause acts as a laboratory cold trap condensing out 

water and preventing it from going above the ozone layer 

27 

rsl.j^,NTENYIWAALLY "M PRECEDING PAGE BLANK NOT FILMED
250 

200 

.1

EARTH

THERMOSPHEREI 

MESOPAUSE

MESOSPHERE 

- STRATOPAUSE 

STRATOSPHERE 

- - - TROPOPAUSE

TROPOSPHERE 

p I • I • 

1JU 'WO 600 800 1000 1200 

TEMPERATURE (DEGREES KELVIN) 

U) 

cx

150 

Ui 

0 -j

neli 

Ix 

Ui 

I

50 

VENUS 

EXOSPHERE - 

EXOBASE - 

THERMOSPHERE 

MESOPAUSE 

MESOSPHERE 

+TROPOPAUSE^ 

TROPOSPHERE 

2 

200 

iso 

Ul 

C) 100 

50

0 1 1 I I f't I I I 

0 200. 400 600 800 1000 

Temperature (K) 

Figure 3.1. Temperature structure of Earth (top) (ref. 27a) and 

Venus (bottom) (ref. 28a).

28
cq

W 

cq 

• W 

1)

U) 

0 

o F-

.4-.

LL 

0 a-

> 

EE EEE EE 

4-0 4-0

-.9 

0 

(I) ('1 )-00c'-C'J0 

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W 

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0.0.0.0.0. 

0.0.0.0.0.

(N 

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00 ••VOO 

• U) 

0 V c 

E 

EE Jo 

CL aa L() . 0 

0. 0..•r-o 

'1N-0 c 

I C'J'-0 c-

. .00-

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' 00-'c 

C() 

U)-

> 

- —

Jo 

0-(D 

U) 

H

13: 

IL

— E E E E E 

aaaa 

I 

I- I OC'JLO I 

oNc\JI . . .0.1 

I . 000 0001 

W 0 0 

c 

w U) 

a: U)

U) 

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ON 

(0c'J 

cc 

a- a0 

WI— 00 

o <OW cj 0 co co LLDWO C4 (\ ciw0Q c'Oww. rr0wOzOi<iiOz0iizxO-...

29 
where it could be readily dissociated by ultraviolet 

radiation. On Venus the planetary cold trap is located near 

100 km and the highly convective atmosphere can transport 

water to altitudes where it can be easily photodissociated. 

Another interesting difference between Earth and Venus 

is the high deuterium to hydrogen ratio (Table 3.1) (ref. 

28b), about a factor of 100 more on Venus than on Earth. The 

measurements are based on data from the lower atmosphere mass 

spectrometer (ref. 32) and inferred from the Orbiter ion mass 

spectrometer (refs. 33,34). This ratio has been used to 

constrain models of the water vapor escape from Venus (refs. 

29-31). Currently, Venus has about 10 to 100 cm equivalent 

liquid water depth in its atmosphere (ref. lc). The carbon 

dioxide and molecular nitrogen inventories per gram of planet 

material for Venus is about one-third less than that of the 

Earth (ref. 31) implying that a similar outgasing has 

occurred, especially of water. There are many ways for gases 

to escape from an atmosphere ranging from thermal (Jeans) 

escape to hydrodynamic flow in which species like HH and HD 

are equally removed. Models (refs. 29,30) for water escape 

differ on whether the water exists on the surface for 

extended period of time (moist greenhouse) or immediately 

evaporates into the atmosphere (runaway greenhouse). In the 

moist greenhouse model there is an earthlike ocean near 100 C 

and an atmosphere of about 1 bar of carbon dioxide. The water 

vapor mixing increases to 20%, the atmosphere warms up and 

hydrodynamic escape of hydrogen ensues entraining heavier 

species like oxygen in the flow. The process works with the 

lower solar constant expected in the early days of Venus. 

The outflow continues until pressure reaches 0.4 bar, after 

several hundred million years, leaving hydrogen to escape by 

normal mass discriminating processes (ref. 71) resulting in 

an iD/H ratio of about 2%.

30
The radiation budget of Venus is shown in Figure 3.2. 

About 80% of the incident light is scattered back to space by 

Mie scattering of the cloud particles and Rayleigh scattering 

of the atmosphere (ref. 280). About 10% is absorbed above 64 

kin, 10% below 64 kin, and 2.5% at the surface (ref. 28d,e). 

With no atmosphere the surface temperature of Venus would be 

about 325 K; with a carbon dioxide atmosphere the temperature 

increases by about 410 K due to the greenhouse effect. For 

the Earth a more modest 35 K results primarily from the 

greenhouse effect of water vapor (ref. 29). The greenhouse 

effect is due to the relative transparency of the atmosphere 

in the visible, where the sun's energy is a maximum, and high 

opacity in the infrared where the Planck curve of the 

planet's surface is a maximum (ref. 27a). Models of the Venus 

atmosphere indicate that the current high temperature is due 

to the carbon dioxide greenhouse effect (ref. 10,35). On the 

left of Figure 3.2 is the radiation budget for Venus and 

Earth (ref. 36a). The average thermal emission is indicated 

in solid lines and the incident energy by a dashed line at 

the top of the atmosphere for Venus and Earth. Venus is about 

60% less than Earth in both categories. The expectation is 

that Venus being closer to the sun should receive about a 

factor of 2 more radiation than the Earth but due to the high 

albedo it receives less energy than the Earth. There is a net 

heating at the equator and cooling at the poles implying that 

dynamics is responsible for transporting the heat from the 

equator to the pole. 

The transport from equator to the pole is hypothesized 

to be due to several single Hadley cells lying above one 

another (Figure 3.3, top) (refs. 280,41). The main cell for 

Venus is at the cloud levels where most of the energy is 

absorbed. In the case of the Earth the major energy 

absorption is close to or at the surface in the tropics. Also 

on Earth, due to the Coriolis acceleration, there is one cell 

31
w 

0 

00 0 LC) H4 LL 

0 c 0O o 

tiJc0 3 

- J-_-. 

LL 0 N w 

E E w w c'i 11 zQ 

I 0 —3 F 

0 (O(0U (D1 

F-W0 3 (90 

ZHWW3 01 w z 

wOcU>Ow IF 3 <(1 

owooj zcr z 

—JOWwH W OW 

0 a. (1) [n w > F 

zWcO a: 

—cr< 0

ol 

0

cz 

0 

U)

Ln 

U) 1 

JF 

za 

>w 

HF 

z 

w w 

00 

00 

z 

I II I Ui 

I Ui

0 

0 0 0 0 0 

In 0 U) 0 U) 

C) 1) N - 

z_wm /XfllJ 3AI1J1au9 

0 0

01 

a U)

32
U 

CLOUD LEI 

HADLEY a 

WESTV 

SUPERRO'

MERIDIONAL CIRCULATION PATTERN 

EYE

EVE. 

POLAR RING POLAR VORTEX

CLOUD 

STRATOSPHERIC 

CELL 

DRIVING CELL 

ON CLOUDS) 

SURFACE LAYER 

CELL 

SUNLIGHT -

PREDOMINANT ZOWAL. PLOW

(WESTWARD) 

CLOUD LAYERS 

HEAT TO DRIVE Wi

CIRCULATION 

Figure 3.3. Hypothesized circulation of the lower atmosphere (top) 

(ref. 28c). Polar "hot" spots (bottom) (ref. 38). 

33
Z 01 

Qo 

cc Uj 

W 

CL 

Co

'C,, 

E 

0) 

a. 

Cl) 80 

60 

N4° 

W

L

S ••

• 

- •l;3qrob S 

- Dt, 

•D S 

- .0 

I I I 

90 -60 -30 0 30 60 90 

Latitude (Deg.) 

80 60 40 20 0 20 40 .60 80 

S N

LATITUDE (deg.) 

Figure 3.4. Measurements of retrograde zonal flow (top) and the meridional flow (bottom) from 

cloud photopolarimeter measurements (ref. 28c). 

34
from the equator to mid-latitudes and a complicated set of 

baroclinic eddies from there to the pole (refs. 27d,37). The 

main circulation is the retrograde zonal flow observed at the 

cloud tops by the cloud photopolarimeter (ref. 28c) shown in 

Figure 3.4 (top). The triangles are Orbiter measurements, 

the solid circles and squares are Mariner observations. The 

solid curve is a solid body rotation of 92 m/s or about 4.8 

day period at the equator. The meridional flow is less than 

10 m/s (Figure 3.4, bottom). At the cloud tops there is a 

quasi-cyclostrophic balance between the meridional pressure 

gradient and the centrifugal force of the zonal flow. Near 

the north pole (Figure 3.3, bottom) there are two infrared 

"hot spots" rotating around each other with a period of about 

2.9 days (ref. 38). The polar collar is cooler than 

surrounding regions. The large scale circulation keeps the 

equator to pole temperatures rather uniform. The wind speeds 

near the surface are less than 10 to 20 cm/s and probably 

reach a maximum of 120 rn/s above 65 km. Balloon measurements 

show that there are vertical winds of up to 12 km/hr at 54 

km, the middle of the cloud layers and considerable 

turbulence (ref. 39). 

Another interesting phenomenon at the cloud tops is the 

sulfur dioxide concentration determined by the ultraviolet 

spectrometer from an absorption feature around 2700 Angstroms 

(Figure 3.5) (ref. ld), plotted as a function of year. The 

measurements occur at about 40 rnb or 69 km and show a 

decrease from the time of orbit insertion until the middle of 

1988. Measurements of the sulfur dioxide below the tops and 

sulfuric acid vapor also show a decrease during this time 

period (ref. 40). The decrease in sulfur dioxide has been 

interpreted as evidence of volcanic activity (ref. 42) 

either by: a) direct injection of sulfur dioxide to 70 km, 

the cloud tops; or b) by gravity wave resulting from an 

explosive eruption mixing the nearly 500 times greater sulfur 

35
Ir 

+ I-

-e ^ LTKIC 

C,) 

0. 

—o 

C) 

I

CC 

-D

• C 

.2 •.2 

(•) L.O 

- C) 

—

ID C'j 75 

C4J w 

o EE 

co

•4- .4-

o + 

0 

E

OR 

+ 

+ 

^

t 

+ 0 

+ co 

L. W -•• -v

co

- 

cm 

co

+ 

+ 

±

+ 

+

+

o 0 0 

(0 It cm 

qdd "os 

o o 

o co

36 
dioxide content below the clouds into the cloud tops, where 

the measurement occurs. The decline results from the gradual 

dissipation of the enhancement. However, it appears that 

effusive eruptions are more characteristic of the surface of 

Venus. The lack of water may prevent explosive eruptions 

(ref. ld) such as occur on the Earth near plate boundaries. 

The sulfur cycle of Venus is shown in Figure 3.6 

(ref. 42,28b). The "squiggles" represent light photons. The 

clouds, consisting of more than 75% sulfuric acid droplets, 

range from 50 to 70 km altitude. There is about one water 

molecule per sulfuric acid molecule. There are three sulfur 

cycles. The fast cycle, occupying about 1 year, involves 

sulfuric acid, sulfur dioxide and sulfur trioxide together 

with atomic oxygen and carbon monoxide derived from the 

photodissociation of carbon dioxide. Oxidation to sulfuric 

acid is aided by hydrogen and chlorine from the 

photQdissociation of hydrogen chloride. The slow cycle, 

occupying about 10 years, involves carbonyl sulfide, hydrogen 

sulfide and allotropes of elemental sulfur. It is thought 

that the yellow color of Venus (Figure 3.7) (ref. 20) is due 

to presence of elemental sulfur. The geologic cycle, lasting 

perhaps 500 million years, converts sulfur dioxide to calcium 

sulfate and then to iron pyrite aided by iron oxide. The 

pyrite is themochemically converted to hydrogen sulfide and 

carbonyl sulfide either under ground or in lava flows. 

The temperature structure of the Venus atmosphere 

derived from various measurements is shown in Figure 3.8 

(ref. 28h). Below 100 km the data are from lower atmosphere 

probes and infrared measurements. The temperature gradient 

below the cloud layers is slightly less than adiabatic (about 

1 K/km less). There are layers around 20 and 50 km that are 

significantly unstable (ref. 41). The optical depth of the 

cloud layers is about 20 to 25 (ref. 43) and turbulence is 

37
0

C! 

8

W/O\ 

fn I (OI'I

o cy

4t 10 

00 __ 

++

I ___ + 

CY

IIT 

IL '- c I 

0 N0 

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CY 

tv .++ i-

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(_-

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+ U)0 

H1;t ^j 4^

II-.. 

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C-0 

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CD ID U) 

(VJ>1) 

f101Mt tJPt

0 0 0 0 0 

It (V) C4 Irl

ORIGINAL PAGE Is ani I I1V OF POOR QUALITY 

39

PRECEDING PAGE BLANK NOT FILMED 
ORIGINAL PAGE IS Fi'ure 3.7. The color of the Liouds (re). :0) ORIGINAL PAGE 

OF POOR QUALITY COLOR PHOTOGRAPH 

41

PRECEDING PAGE BLANK NOT FILMED
200 

180 

160 ( 

q140 

120 

E - 100 

N 

• 80

NOON 

ONMS 

model 

/OAD 

MIDNIGHT 

ONMS 

8:30 AM 

BNMS 

model

PROBES 

o 7:38 AM, 4°N 

o 6:46 AM, 31°S 

o 0:07 AM, 270S 

t 3:35 AM, 59°N 

CLOUDS 

UPPER 

- MIDDLE 

- LOWER 

all 

—Il

100 200 300 400 500 600 70C 

To 

Figure 3.8. Temperature measurements of the Venus atmosphere (ref. 28h). 

4.1 

01 

17

43 

bLAM PRECEDING PAGE BLANK NOT FILMED
observed near 60 km from radio occultation measurements (ref. 

44). The lower atmosphere is rather uniform in temperature 

horizontally, a reflection of the large thermal inertia of 

the atmosphere and the fact that the time scale for dynamic 

processes is much less than the radiative time scale (ref. 

27d). On Earth the oceans show very little day to night 

temperature difference for the same reason. In the 100 to 

140 km region there are wave-like structures in the 

temperature. Above 140 km temperatures from an empirical 

model of the neutral mass spectrometer data show a 

temperature of about 320 K at noon and about 130 K at 

midnight. Temperatures from satellite drag and the mass 

spectrometer on board the bus are also shown. 

The region from 100 to 140 km is a transition region 

from a mixed atmosphere below to one in diffusion equilibrium 

above (ref. 27d). In a mixed atmosphere all species, in the 

absence of chemistry, adopt the same density scale height and 

have a constant mixing ratio. This is due to the fact that 

the time to establish diffusion equilibrium over the distance 

of a scale height is large compared to the time scale of 

dynamic processes like wind, and turbulence. In diffusion 

equilibrium the reverse is true and each species acts 

independently of other species, adopting a scale height 

characteristic of its mass. The point where the eddy 

diffusion coefficient is equal to the molecular diffusion 

coefficient is termed the turbopause and for helium at noon 

it is about 114 km (ref. 45). 

The effect of diffusion equilibrium on the densities 

measured in the exosphere is shown in the altitude profile of 

Figure 3.9 (bottom) (ref. 46). The scale height is inversely 

proportional to the species mass and proportional to the 

temperature. Note that atomic oxygen is dominant above 160 

km, not carbon dioxide; at night helium is dominant above 

44
DIURNAL EXOSPHERIC TEMPERATURE 

400, 1 .1 

• •#_. :. . 

.

• - • •.• •.4• ••. • • 

• •_?.•;• . . .•._• ':" 

•_?./ • •• • • • :., 

• •• •. 

.•. ••

• 

. , .

• :

.•

: 

• 

300 

w

200 

cc 

w

100

ru

6 12 18 

LOCAL SOLAR TIME (hr) 

DAYTIME ALTITUDE VARIATION 

240 

22 

Ui 

II--J

16

106 10 7 108 109 1010 

AMBIENT DENSITY (cm-3) 

Figure 3.9. Neutral mass spectrometer exospheric temperatures derived from 

atomic oxygen (top) and the altitude variation of the composition at noon 

(bottom) (ref. 46). 

140 

10 5

45
about 180 km. 

Exospheric temperatures derived from the scale heights 

of atomic oxygen are shown in the top panel of Figure 3.9 as 

a function of local solar time. It takes 225 days, the 

orbital period (Table 1.1), to cover one cycle in local solar 

time (ref. 281). The periodic maxima observed during the 

daytime are a result of the 29 day solar rotation in the euv 

heating of the thermosphere. 

The diurnal variation of carbon dioxide and helium are 

shown in Figure 3.10 (ref. 28b). The data are shown at a 

fixed altitude of 167 km. In carbon dioxide the maximum 

density occurs at noon where the sub-solar heating is a 

maximum. There is a large day to night ratio and a steep 

density gradient near the terminators. The strong gradients 

in temperature and density at the terminators imply a strong 

pressure gradient and winds approaching the velocity of Sound 

(about 200 m/s in carbon dioxide (ref. 46)). However, helium 

peaks near 5 am in the morning not near noon. This is due to 

the combined effects of wind-induced diffusion and superrotation of the atmosphere (ref. 47). Horizontal flow in 

diffusion equilibrium is such that the height integrated flux 

is proportional to the species scale height (ref. 27a,e). 

Vertical flow downward through the turbopause is proportional 

to the mean mass scale height. The effect of wind-induced 

diffusion is to create a light mass gas (i.e. hydrogen and 

helium) bulge at midnight. Super-rotation of the atmosphere 

shifts the bulge to 5 am in the morning. A spectral model 

(ref. 47) of the Venus thermosphere found the super-rotation 

period to be between 4 and 8 days with a best fit period of 6 

days. The direction is westward like that of the lower 

atmosphere and it appears that the whole atmosphere of Venus 

super-rotates. A recent conjecture (ref. 48) suggests that 

planetary atmospheres should super-rotate. 

46
N EUTRAL THERMOSPHERE 

108

DIURNAL DENSITY VARIATION 

167 KM 

Co2

. b

* 

C?: 

E 

0

106 

W 

io 

109 

Fw108

- • • •

:. •• . — •%• •

•••••• ••l 

•_ 

•s •.

•

S

•

S •. •.••__ 

.I_t .• . . •_e • - ••• •

• •. 

S

•

•

•

•S • %•. •• S 

,• 4 5z5.

S. 

• .l_ 

106 

He 

i L 

'0 6 12 18 

LOCAL SOLAR TIME (hr) 

Figure 3.10. Densities from the neutral mass spectrometer for carbon dioxide (top) 

and helium (bottom) at a fixed altitude as a function of local solar time (ref. 28b). 

47
A pre-dawn bulge is also seen in neutral hydrogen 

(Figure 3.11 ,top)) (ref. 36b). Neutral hydrogen at 165 km 

was derived from charge exchange equilibrium using ion mass 

spectrometer measurements of 0+ and H+ and neutral mass 

spectrometer measurements of 0 (ref. 49). As can be seen from 

Figure 3.11 (bottom) the bulge in neutral hydrogen is due to 

the bulge in H+ (ref. 51). The hydrogen bulge has also been 

seen in the Lyman-alpha data from the ultraviolet 

spectrometer (ref. 50). 

Figure 3.12 shows a map of the airglow due to nitric 

oxide, the delta (0,1) band at 2365 A, from ultraviolet 

spectrometer measurements (ref. 52). The horizontal axis is 

local solar time: midnight is at the center, 6 hours at the 

left and 18 hours at right. The vertical axis is latitude: 

the north pole is at the top and the south pole at the bottom 

with the equator in the center. Yellow is the maximum 

emission and blue the minimum emission. The maximum emission 

altitude is near 110 km and is due to the recombination of 

atomic nitrogen and atomic oxygen. These species are created 

on the dayside, transported at high altitude across the 

terminator to the nightside and subside to recombine at lower 

altitude. The nitric oxide glow is a tracer of the 

circulation and the signal maximum occurs at the local time 

where the vertical transport is a maximum. 

The transport is displayed in a contour map of the 

horizontal winds from a spectral model of the thermosphere 

(ref. 47) at 170 km, Figure 3.13. There is an upwelling near 

the subsolar point on the equator and flow across the 

terminator with a speed near 100 m/s to a subsistence point 

near 3 am in the morning. The circulation probably closes 

around 90 km. In current models of the thermosphere (refs. 

47,53) the low nightside temperature is generated by slowing 

48
108 

E

io 

I

10

Neural H 

01 MS 165 km

O+H ---H+O 

—OUVS Lya 

1041 I I I I I I I 

02 4 6 8 10 12 14 16 18 20 22 24

HOUR ANGLE 

DIMS ALTITUDE 200 I 

io 

C-,

io 

IU, 

uJ 

9 102

10 

DAWN NOON DUSK 0 - 

I

0-0+ 

LA • 

A A. S

L02+ 

AAAAA 

900,000

.

o 0 

••

1

0 

A 

o 0

AAAA 

AA

OO 0 (DA A 

0 000 0 OO 

0

0

0

101 0

100

180 160 140 120 100 80 60 40 20 20 40 50 80 100 1ZU 14U ibU 

90 0 90 180 

SOLAR ZENITH ANGLE (DEG) 

Figure 3.11. Neutral hydrogen derived from measurements of the ion and neutral mass 

spectrometers and from Lyman-alpha measurements (top) (ref. 50). The diurnal variation 

of H+ and 0+ densities (bottom) (ref. 5 1).

49 
Figure 3.12. Nitric oxide airgiow on the nightside (ref. 52). 

ORIGINAL PAGE IS 

OF POOR QUALITY

ORIGINAL PAGE 

51 COLOR PHOTOGRAPH 

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the flow across terminator. This lowers the nightside energy 

input due to adiabatic compressional heating which is 

balanced primarily by the 15 micron carbon dioxide cooling 

and, at higher altitudes, by conduction. Rayleigh friction is 

added to the momentum equation which slows down the flow 

across the terminator and amount of heat being supplied to 

the nightside. The effect is assigned to gravity waves which 

propagate upwards, break at high altitude and modify the 

horizontal flow. Like eddy diffusion, Rayleigh drag is 

treated as an adjustable parameter to make the model results 

match the solution which nature has already provided. 

There is evidence of waves in the neutral density 

measurements from the neutral mass spectrometer (ref. 54). 

Figure 3.14 shows the density variation, with the altitude 

effect removed, as a function of time near the dusk 

terminator. Wave-like structures are seen in the various 

gases measured with helium out of phase with the other 

species. The waves travel slowly and appear stationary with 

respect to the satellite speed (nearly 10 km/s at periapsis). 

The actual direction of travel cannot be determined. A 

gravity wave model for the thermosphere (ref. 55) confirms 

that the waves are gravity waves with a period between 1/2 to 

1 hour and an excitation source in the lower atmosphere. 

Higher frequency waves are also seen in the plasma near the 

region of the terminator but show little correlation with the 

lower frequency neutral density waves (ref. 56). The peak in 

the wave activity for carbon dioxide occurs near the 

terminator where turbulence might be expected (refs. 54,46). 

Longer period waves have also been observed in the 

temperature deviations deduced from infrared observations at 

90 km and drag density at 115 km (Figure 3.15) (ref. 57). 

The measurements differ in longitude by a little more than 

180 degrees and are apparently in phase with each other. The 

54
N ro 

Ciç.4 

CD 

N.uj 

u--

c'J

03 tn

'1 

> 

4—

I-

-J 

41) 

41) 

4-

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-J 

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41) 

(.1.; 

41) 

I4141 

LL 

Ix LLJ 

C', 

uJ 

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>-

F-

> 

cc 

z 0>-• 

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—J 

cc 

Iw 

z

I I I I 

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N.

a 

o i 0 Z Ci 

I I I I

ç.4 c'4 

I I. 

(viva auIoovDo1 io 

55
5.7 DAY INTERVALS 

-x 

>-..... 

E 

I—cs 

'E 3.

-s 4.

0.

DP 0 0 0 

c:i I' •i •ii 

z, uQ 

c140 cr1— ,r',-' 11⁄4J\J 

60 CL Uj 

.n '-'

Wb II 21 31 10 20 2 12 22 

JAN. FEB. MARCH 

1979 

2 A so km EXOSPHERIC TEMPERATURE H55 km) 

140 

z 

—Q. 

LJ 2

1200 

wUJO 

Z -

______ LLJ _________

100' a0

-

80 

C,--

B 

- 3r CLOUD TOP

80km 

Li km 

O0

ZL 

'C0 

6

I 

7 8 9 10 II 12 

JANUARY 1979 

Figure 3.15. Inferred temperature variations at 90 km and 155 km (ref. 57).

56 
period is about 5.6 days. It is thought that the 

perturbations are caused by planetary scale waves propagating 

upward from the lower atmosphere (ref. 280). 

57
Figure 4.1 (ref. 36c) shows the relative ion composition 

during daytime measured by the ion mass spectrometer. Note 

that the major ions are atomic oxygen and molecular oxygen 

not carbon dioxide. This is due to ion chemistry as is shown 

in Figure 4.2 (ref. 27f,71). Carbon dioxide ions are rapidly 

converted to atomic oxygen and molecular oxygen ions through 

atom-ion interchange or charge transfer. Dissociative 

recombination restores the neutral species. Ions can also 

participate in other neutral reactions (ref. 27e,71). For 

example, the charge exchange of hot protons with neutral H in 

the hydrogen bulge can lead to thermally excited neutral 

hydrogen atoms forming a hydrogen corona with some atoms 

having enough energy to escape. Other neutral reactions can 

also contribute the hydrogen corona. An oxygen corona is 

formed from the dissociative recombination of 02+; Atomic 

oxygen atoms can also be ionized or photoionized, picked up 

by the local magnetic field, and transported elsewhere on the 

planet or in some cases even escape. 

Coronas are observed (ref. 36b) in H, C, N and 0 (Figure 

4.3). As can be seen for 0 the non-thermal or "hot" oxygen 

corona forms an extended atmosphere at high altitudes which 

is important for mass loading of the solar wind (refs. 7,58). 

In mass loading, "hot" oxygen is photoionized and gets 

attached to the solar wind magnetic field, slowing it down. 

Although "hot" hydrogen is also present in large 

concentrations, it is the more massive oxygen atom that is 

important for the process of mass loading. The data in the 

figure reflects solar maximum conditions. 

Figure 4.4 (refs. 59,65) shows the solar wind 

interaction with the ionosphere of Venus. The solar wind is a 

low density plasma, 10 to 15 particles/co, primarily 

58
I I I

tm 

CT) 

CD 

w 

'-I 

Li 

CD 

z 

fX 

NJ 

(i)

--4 

tm 

(\J -4 

Li 

Ci 

< E 

D 

Z > 

cn

4-

I4-4 

Li 

> 0 

'-4 

i-. E 

LL 

-J 

4-J 0 

4-

tm 

tm 

Lfl CT)

-4 

r) 

upw

(I'4>i) BOflhIflV 

59 
ION COMPOSITION (O, o MAJOR IONS) 

PRODUCTION 

CO2 + hv -*CO+ e )<900A J'7.5x10 7 s 

O+hvO++e A<911A J"4x10 7 s 

ATOM—ION INTERCHANGE 

O + CO +

-+0+

 + CO k=9.6x10' 1 cm -3/s 

or CHARGE TRANSFER 

O+CO-O+CO2 

0

k=1.6x101° cm 3/s 

+ + CO2 -' O+ CO k=9.4x1 0_10 cm3/s 

DISSOCIATIVE RECOMBINATION 

CO+e -CO+O k"3x107 CM 3/s 

O+e - O+O k"3x107 cm3/s 

H: CORONA/ESCAPE

* H+H -+H + +H (Charge exchange) 

0* + H -^ H* + 0* (Knock—on sputtering) 

+* * 

O + H -1. 0+ + H (Charge exchange) 

0+ + H2 - OH + + H* (Ion—neutral) 

OH+ + e Q + H* (Dissociative recombination) 

0: CORONA 

SOLAR WIND PICKUP 

O+hv,O++e 

O+eO++2e

(Dissociative recombination) 

0+ picked up by magnetic field 

Figure 4.2. Various ion processes (refs. 27f, 71). 

M.
61

8- 8 Lt\

CJ '-4 

a 

NJ 

%0 

CD 

a

c. 

- 

CD 

CD 

C) I 

-

-

C)

0 

0 

C.) 

cI 

C 

z 

(-) 

0 

0 

0 

C.) 

H 

cq 

ci)
I' I, / / / / 

= --S...... \ 2 0 • s A — I A C) i I 1' 

0) 'I 1 C) II I / - -

/ I' II Ii •::.

II ii I

II C)

C.) •1 Q 

\ 

C) —' ' C)

/ I \ c. / cn / 

\\\ 

o

cl 

-

S5

.v_ 

/ 

I, Q•) / 

, 

,

- 

LL. U)

/ + Q 

/ °E LU Cl)- CJ

> 

C4 0 c 

(Ad) six' Luo 93uDsI 

hi 

I

C,)

C) 

I-. 

IC

C) (I) > 

0 

C.) 

CU 

C) 

ICU 

0 

C) 

C.) 

- 

"I
hydrogen, with a speed of about 400 km/s. The interplanetary 

magnetic field makes an angle of about 40 degrees with 

respect to a line connecting Venus and the Sun. The flow is 

supersonic, forming a bow shock about 1.3 radii of Venus at 

the sub-solar point. On earth the equivalent position is 

about 14-16 radii of Earth due to the presence of the Earth's 

magnetic field. The flow is turbulent across the the shock. 

The ionopause (ref. 69) is the boundary between the shocked 

solar wind and the ionosphere. It is approximately the 

balance point between the dynamic pressure of the solar wind 

and the ionospheric pressure. At the sub-solar point the 

ionopause is around 300 km. The mass loading is a maximum 

around 400 km (ref. 58) and the effect is to make the bow 

shook move outward (ref. 60,72). 

r%3
5. SOLAR ACTIVITY EFFECTS 

The effect of periapsis moving upward is shown in Figure 

5.1 (ref. 61). There are several consequences of this fact: 

a) it is no longer possible to measure the neutral atmosphere 

and main ionosphere at low altitude; b) the nightside 

ionosphere is sampled at higher altitudes in a region termed 

the iontail; and c) the solar activity changes from solar 

maximum to solar minimum conditions as indicated by an EUV 

index derived from the electron temperature probe (refs. 

60,69). The EUV index is a photo emission measurement (ref. 

70) for wavelengths less than about 1300 Angstroms. A little 

more than one-half of the contribution comes from the Lymanalpha line. Wavelengths in this range are responsible for 

heating and ionization of the atmosphere. The corresponding 

10.7 cm radio flux index is about 200 at solar maximum and 70 

at solar minimum (ref. 69). 

The bowshock position as a function of solar activity is 

illustrated in Figure 5.2 (ref. 60). The position is measured 

at the terminator since the sub-solar point is not accessible 

at solar minimum due to the high altitude of periapsis. As 

solar activity decreases the terminator altitude moves inward 

(top). The actual distance is plotted in the bottom of the 

figure. The cause of this decrease is the decrease in the 

mass loading. At lower solar activity, the dissociative 

recombination of 02+ decreases due to the lower EUV input, 

resulting in a decrease in the "hot" oxygen corona and in the 

mass loading. There is also a decrease in the ionosheath or 

magnetosheath pressure near the terminator allowing the solar 

wind magnetic field to move closer to the planet. There is 

evidence that the atomic oxygen emission deduced from the 

130.4 nanometer line has decreased from solar maximum to 

solar minimum as observed by the ultraviolet spectrometer 

(Figure 5.3) (ref. id). The emission, including both cold 

64
0) 

co 

NC co 

 Wco 

>

Co 

Co 

0) 

N-

— - 

5 

4: 

-I 

- - 

- - 

•• • ..;:; 

:

- - 

-

.: .

-: I 

0 0 0 c CC.-

a) 

C-. 

Ia) 

0 

0 

Ca 

Ca 

a) 

> 

> 

Ca 

ICa 

0 

Ca 

a) 

Ca 

0. 

I-. 

Ca 0. 

a) •0 

a) 

C-. 

-J 

(I..s ..ui3 suooqd10j) AS13A 

Co r- CD LO - OD

CQ-:00) 

C) 

0 0 0 0 0 

LI) 0 U) 0 II) 

c.'j C') - - 

(uDf) opmillV s!sdud 

65 
'I 

I

2.4 R 

Solar Cycle Effects on Venus' Bow Shock 

S.

Solar mm 

Solar max 

250 

200 

'C 

E 

C)

150 

a, 

C) 

E

100 

0 

a 

C, 

C 

CO

So 

0'

2.6 

2.5 

> 

CC

2.4 

0 

CU 

- .0 2.3 

CO 

0

2.2 

2.1

I I II I I I - 

Bow shock 

0

EUV flux 

10.7 cm flux 

o—. Sunspot numbers -

* Venera 9/10 

rI

I I I I I I - - 0.6 

1.8 

1.6

C) 

1.2

LL 

0.8 

1975 1977 1979 1981 1983 1985 1987 1989 

Year 

Figure 5.2. The bow shock position as a function of solar activity (ref. 60).
I

10- • Atomic Oxygen 

(I) - 

(I) 

— 6 

LM 

0) 

.-

' 

2-

78 180 '82' 1841 '86' 88 

Carbon Monoxide 

CI) 

Cl)

0.5- 

r. 0.3- 139 nm

moo 

0)

''SoIar 

122 nm 

0.1 1 II 

0 100 200 300 

Solar Activity Index 

Figure 5.3. Atomic oxygen and carbon monoxide emission as a function of year 

and solar activity (ref. id).

67
and "hot" oxygen contributions, implies a decrease in the 

oxygen corona and in the mass loading. 

Figure 5.4 shows the various processes occurring in the 

ionosphere of Venus (ref. 69): the bow shook and its 

interaction with the ionosphere; the formation of ions on the 

dayside, transport across the terminator; and subsistence or 

escape (ref. 62) on the nightside. The nightside is very 

erratic with two more or less permanent features called 

ionospheric holes or troughs. Two example orbits are shown 

in 1980 (solar maximum) and in 1986 (solar minimum). At solar 

minimum the nightside ionosphere at high altitude ("iontail") 

is sampled. In this region atomic oxygen ions of 

suprathermal energy (9-18 eV) and higher energies (greater 

than 40 eV) have been observed with enough energy to escape 

Venus (ref. 62). 

The average electron density in the nightside iontail 

region (1400 to 2500 km) is shown in Figure 5.5. The average 

for each nightside tail pass is plotted along with the 

average EUV index (ref. 61). As solar activity decreases, the 

average electron density decreases. The relative roles of the 

variation with solar EUV, solar wind pressure change, 

transport across the terminator and the nightside ionization 

source is not clearly understood. At solar maximum transport 

across the terminator from the dayside to niglitside is 

sufficient to maintain the nightside against loss due to 

recombination (ref. 28j). At solar minimum the situation is 

less clear and it may be that nightside ionization sources 

are relatively more important. Two possible sources have 

been identified: a) a 10-50 eV electron flux whose source is 

most likely the solar wind; and b) a downward flux of 0+. 

The electron flux is most likely responsible for the

nightside aurora seen in atomic oxygen at 130.4 nm (ref. 6). 

68
z 

0 '3 UA

I 

LU 0 -' 

cc LL. :D -^7- 16 

LU

—0

co 

# 

cr k Psi\J4v\A 

cr 

cr fl I Lu L.

I—i 

Lu 0 I U) cr.

0o It z I I 

04( 11 d \l / 

cr

- 

-

C 

I.-. 

— C. 

C C 

IC 

C 

I-. 

C. 

0 

H 

Ito 

A 

ORIGINAL PAGE IS o

9ORIGINAL PAGE 

OF POOR QUAUTY COLOR PHOTOGRAPH 
o 

C\) 2(J) 

— 0

(0 Co 0 

C

Co 

Co 

OD 

co1

GD 

I-

>.. 

o 

o

0 

C)

0 

o 

o

ni 

o 

oC 0 

0 

I0 

0 

co 

(0 

w

+ 

Lo 

V00 t 

(0 > 

CD 

GD

I I I I

0 

0 0 0 0 0 0 0 0 

U) 0 L0 0 11) 0 U) 

Co C') CJ C\J — - 

en 

Zi

71

PRECEDING PAGE BLANK NOT FILMED 
The auroras are shown in Figure 5.6 for 3 different days. The 

crescent at the top of each image is due to the dayside 

resonant scattering of sunlight and photoelectron emission. 

The aurora on the nightside is highly variable as can be seen 

from the variation in emission intensity. 

Although in situ measurements of the low altitude 

ionosphere are not possible at solar minimum, due to the high 

periapsis altitude, radio occultation measurements can be 

used to probe this region. Electron density profiles for 

1980, at solar maximum, and in 1986, at solar minimum, are 

show in Figure 5.7 (ref. 63). The peak density dropped by 

about a factor of 1.5 from solar maximum to solar minimum 

implying that the solar euv ionization source was reduced by 

about a factor of two. Photochemical equilibrium holds below 

about 180 km and in this case radio occultation measurements 

can be used to infer the neutral temperature above the ion 

peak .near 140 km (ref. 64). The solar maximum minus minimum 

exospheric temperature change is about 60 K (ref. 64), that 

from empirical models (refs. 45,36b) about 55 to 70 K and 

that from theoretical models (refs. 66,67) about 65 to 70 K. 

However, all of these changes are smaller than that observed 

for the Earth's thermosphere (ref. 68) of about 420 K. 

Clearly the Venus exospheric temperature is less sensitive to 

solar cycle change than the Earth. The strong 15 micron 

cooling due carbon dioxide buffers the response of the 

exosphere to changes in the solar euv activity (ref. 67). 

72
S 

M

t

Figure 5.6. Nightside atomic oxygen aurora (ref. 6). 

ORIGINAL PAGE Is 73 

OF POOR QUALITY

ORIGINAL PAGE

COLOR PHOTOGRAPH 
800 

600 

E 

w

400 

I200 

0 

.1

P-V RO EXPERIMENT 

1980

1986 N

104 10 106 

SOLAR ZENITH ANGLE: 600-700 

AVERAGE ELECTRON DENSITY (cm3) 

Figure 5.7. Electron density profiles from radio occultation (ref. 63). 

P,7.11 NTENTIOMMIY

75

PRECEDING PAGE BLANK NOT FILMED 
Table 5. 1. Neutral Exospheric Temperature Change at Solar Maximum and Solar Minimum Conditions 

NEUTRAL EXOSPHERE TEMPERATURE 

• LuT=T(Solar maximum) - T(Solar minimum) 

Radio Occultation T=6OK 

Hedin et al. empirical model T=55K 

VIRA empirical model 1T=75K 

Dickenson & Bougher 1—D T=65K 

NCAR-2D ET=70K 

EARTH (MSlS) tT=420K 

(150 km, SZA=550-750) 

(F, 0.7=200 to 70) 

(F10 7=200 to 70) 

(F, 0.7=200 to 74) 

(F, 0.7=200 to 74) 

(F, 0.7=200 to 70) 

• Venus temperature less sensitive to solar cycle change than Earth 

• NCAR model results at solar minimum compared to maximum: 

Reduced EUV (X<105 nm) inputs by factor of 3 

Reduced 1 5—gm cooling; reduced wind speed (20-30 m/s) 

Reduced NO (ô band ) night airgiow by factor of 3

Night side temperature about same; minimum at 0200 hours LST 

76
A large body of data has been accumulated on Venus, its 

atmosphere and ionosphere by the Pioneer Venus Orbiter. The 

data base now covers almost an entire solar cycle. The 

reentry period 1992 will allow further measurements of the 

neutral atmosphere and low altitude ionosphere. At the end of 

this time the Orbiter will fade away to a well deserved rest 

after having performed its tasks as a good and faithful 

servant.

77
la. Cohn, L., 1989, 

Discovery, ed. L. Cohn, NASA/Ames Research Center, 

Table 2. 

lb. Sjogren, J., 1989, Pioneer Venus Orbiter -Ten Years of 

Discovery , ed. L. Cohn, NASA/Ames Research Center, 

Chapter 4.6.2 (The Surface and the Interior: Gravity 

Field). 

lo. Hunten, D.M., 1989, 

Discovery , ed. L. Colin, NASA/Ames Research Center 

Chapter, 4.7 (Venus: Lessons for Earth). 

id. Stewart, A.I.F., 1989, Pioneer Venus Orbiter - Ten Years 

of Discovery, ed. L. Cohn, NASA/Ames Research Center, 

Chapter 4.5 (The Atmosphere Seen from Orbit). 

le. Brace, L.H., 1989, Pioneer Venus Orbiter -Ten Years of 

Discovery, ed. L. Cohn, NASA/Ames Research Center, 

Chapter 4.3 (The Dynamics of the Ionosphere). 

if. Cohn, L., 1989, Pioneer Venus Orbiter - Ten Years of 

Discovery , ed. L. Cohn, NASA/Ames Research Center, 

Tables 7.0.1,8.0.1. 

2a. Fimmeh, R.O., L. Cohn and E. Burgess, 1983, Pioneer 

Venus, NASA SP-461, NASA Scientific and Technical 

Information Branch, Chapter 2. 

2b. Fimmel, R.O., L. Cohn and E. Burgess, 1983, Pioneer 

Venus, NASA SP-461, NASA Scientific and Technical 

Information Branch, Chapter 8. 

2c. Fimmeh, R.O., L. Cohn and E. Burgess, 1983, Pioneer 

Venus, NASA SP-461, NASA Scientific and Technical 

Information Branch, Chapter 6. 

3. Cohn, L., 1989, Pioneer Venus Bibliography, Pioneer 

Missions Office, Ames Research Center, Moffett Field 

Calif. 

4. Beatty, J.K., 1978 "Encounters with Venus," Sky and 

Telescope, 56(6), pp. 484-486. 

5. Eberhart, J., 1986, "The Night Skies of Venus: Another 

Kind of Aurora," Eberhart, Science News, 130(25), 

pp. 364-365.

78
6. Phillips, J. L., A. I. F. Stewart and J. G. Luhman, 1986, 

"The Venus Ultraviolet Aurora: Observations at 130.4 

NM," Geophysical Research Letters, 13(10), 

pp. 1047-1050. 

7. Luhmann, J.G., 1986, "The Solar Wind Interaction with 

Venus," Space Science Reviews, 44, pp. 241-306. 

8a. Meszaros, S.P., 1983, Planetar y Size Comparisons: A 

Photographic Study, NASA TM-85017, NASA photo number 

83H228, p. 2-30. 

8b. Meszaros, S.P., 1983, Planetary Size Comparisons: A 

Photographic Study, NASA TM-85017, NASA photo number 

83HC206, p. 2-31. 

9. Phillips, J.L. and C.T. Russell, 1987, "Upper Limit on 

the Intrinsic Magnetic Field of Venus," Journal of 

Geophysical Research, 92(A3), pp. 2253-2263. 

10. Parker, E.N., 1983, "Magnetic Fields in the Cosmos," 

:Scientific American, 249(2), pp. 44-54. 

11. Stevenson, D.L., T. Spohn, and G. Schubert, 1983, 

"Magnetism and Thermal Evolution of the Terrestrial 

Planets," Icarus, 54, pp. 466-489. 

12. Pettengill, G.E., D.B. Campbell and H. Masursky, 1980, 

"The Surface of Venus," Scientific American, 243(2), 

pp. 54-65. 

13. Masursky, H., E. Eliason, P.G. Ford, G.E. McGill, G.E. 

Pettengill, G.G. Sohaber and G. Schubert, 1980, "Pioneer 

Venus Radar Results: Geology from Images and Altimetry," 

Journal of Geophysical Research, 85(A13), 

pp. 8232-8260. 

14. "Fractured 

257(1), p. 

15. Saunders, 

of the Ter 

16. Briggs, G. 

Photograph 

Press, pp.

Aphrodite," 1987, Scientific American, 

19. 

I.S. and M.H. Carr, 1984, "VENUS," in Geology 

restrial Planets, NASA SP-469, pp. 57-77. 

and F. Taylor, 1986, "VENUS," in Cambridge 

Lc Atlas of the Planets, Cambridge University 

44-71.

79
17. Greely, R., 1985, "VENUS," in Planetary Landscapes, 

Allen and Unwin, pp. 132-260. 

18. Burgess. B., 1985, VENUS, Columbia University Press, 

N.Y., Chapter 6. 

19. Beatty, J.K., 1982, "VENUS: The Mystery Continues," 

Sky and Telescope, 63(2), pp. 134-138. 

20. Meszaros, S.P.,. 1982, 

ystem as Viewed. by NASA Spacecraft, Goddard Space 

Plight Center Library, NASA photo number 79HC46. 

21. Bazilevskiy, A.T., 1989, "The Planet Next Door," 

and Telescope, 77(4), pp. 360-368. 

22. "The Stuff of Venus: Taste-tests and Turmoil", 1982, 

Science News, 121(13), PP. 214-215. 

23. "The Basalts of Venus", 1983, Scientific American, 

249(2), pp. 58-59. 

24. "The Other Side of Venera 14: Capturing Venusian 

Evolution?," 1982, Science News, 121(15), P. 245. 

25. J. Eberhart, 1982, "Eyes on Venus: A New Dimension", 

Science News, 121(15), pp. 248-249. 

26. Pieters, C.!'!., J.W. Head, W. Patterson, S. Pratt, J. 

Garvin, V.L. Barsukov, A.T. Basilevsky, I.L. 

Thodakovsky, A.S. Selivanov, A.S. Panfilov, Y.M. Gektin 

and Y.M. Narayeva, 1986, "The Color of the Surface of 

Venus," Science, 234, Pp. 1379-1383. 

27a. Chamberlain, J.W. and D.M. Hunten, 1987, Theor y of 

Planetary Atmospheres, Academic Press Inc., San Diego 

Ca., Chapter 1 (Vertical Structure of the Atmosphere). 

27b. Chamberlain, J.W. and D.M. Hunten, 1987, Theory of 

Planetary Atmospheres, Academic Press Inc., San Diego 

Ca., Chapter 4 (Planetary Astronomy). 

27c. Chamberlain, J.W. and D.M. Hunten, 1987, Theory of 

Planetary Atmospheres, Academic Press Inc., San Diego 

Ca., Chapter 6 (Airgiow, Auroras, Aeronomy). 

80
27d. Chamberlain, J.W. and D.M. Hunten, 1987, Theory of 

Planetary Atmospheres, Academic Press Inc., San Diego 

Ca., Chapter 2 (Hydronamios of Atmospheres). 

27e. Chamberlain, J.W. and D.M. Hunten, 1987, Theory of 

Planetary Atmospheres, Academic Press Inc., San Diego 

Ca., Chapter 7 (Stability of Planetary Atmospheres). 

27f. Chamberlain, J.W. and D.H. Hunten, 1987, Theory of 

Planetary Atmospheres, Academic Press Inc., San Diego 

Ca., Chapter 5 (Ionosphere). 

28a. Hunten, D.M., 1983, in Venus, ed. D.M. Hunten, L. 

• Cohn, T.M. Donahue and V.I. Moroz, University of 

Arizona Press, Tucson Az., pp. vii-viii. 

28b. von Zahn, U., S. Kumar, H. Niemann, R. Prinn, "13. The 

Composition of the Venus Atmosphere," 1983, in Venus, 

ed. D.M. Kunten, L. Cohn, T.M. Donahue and V.I. 

• Moroz, University of Arizona Press, Tucson Az., pp. 299-

430. - 

28c. Schubert, G., "21. The General Circulation and the 

Dynamical State of the Venus Atmosphere," 1983, in 

Venus, ed. D.M. Kunten, L. Cohn, T.M. Donahue and 

V.I. l4oroz, University of Arizona Press, Tucson Az., 

pp. 681-765. 

28d. Taylor, F.W., D.M. Hunten, and L.V. Ksanfomaliti, "20. 

The Thermal Balance of the Middle and Upper Atmosphere," 

1983, in Venus, ed. D.M. Hunten, L. Cohn, T.M. 

Donahue and V.I. Moroz, University of Arizona Press, 

Tucson Az., pp. 650-680. 

28e. Tomasko, M.G. "18. The Thermal balance of the Lower 

Atmosphere of Venus," 1983, in Venus, ed. D.M. Kunten, 

L. Cohn, T.M. Donahue and V.I. Moroz, University of 

Arizona Press, Tucson Az., pp. 604-631. 

28f. Phillips, R.J. and M.C. Maim, 1983, "10. The Interior 

of Venus and Tectonic Implications," inVenus, ed. D.M. 

Kunten, L. Cohn, T.M. Donahue and V.I. Moroz, 

University of Arizona Press, Tucson Az., pp. 159-214. 

81
28g. Moroz, V.1., 1983, "5. Summary of Preliminary Results of 

the Venera 13 and Venera 14 Missions," in Venus, ed. 

D.M. Hunten, L. Cohn, T.M. Donahue and V.I. Moroz, 

University of Arizona Press, Tucson Az., pp. 45-68. 

28h. Seiff, A., 1983, "11. Thermal Structure of the 

Atmosphere," in Venus, ed. D.M. Hunten, L. Cohn, 

T.M. Donahue and V.I. Moroz, University of Arizona 

Press, Tucson Az., pp. 215-279. 

281. Cohn, L., 1983, "2. Basic Facts," in Venus, ed. D.M. 

Kunten, L. Cohn, T.M. Donahue and V.I. Moroz, 

University of Arizona Press, Tucson Az., pp. 10-26. 

28j. Brace, L.H., H.A. Taylor, T.I. Gambosi, A.J. Ihiore, 

W.C. Knudsen and A.F. Nagy , 1983, "23. The Ionosphere 

of Venus: Observations and their Interpretation," in 

Venus, ed. D.M. Hunten, L. Cohn, T.M. Donahue and 

V.I. Moroz, University of Arizona Press, Tucson Az., 

779-840. 

29. Kastings, J.F., O.B. Toon and J.B. Pollack, 1988, "How 

Climate Evolved on the Terrestrial Planets," Scientific 

American, 258(2), pp. 90-97. 

30. Kastings, J.F., J.B. Pollack, and T.P. Ackerman, 1984, 

"Response of Earth's Atmosphere to Increases in Solar 

Flux and Implications for Loss of Water From Venus", 

Icarus, 57, pp. 335-355. 

31. Kumar, S., D. 14. Hunten, and J. B. Pollack, 1983, 

"Nonthermal Escape of Hydrogen and Deuterium from Venus 

and Implications for Loss of Water," Icarus, 55, pp. 

369-389. 

32. Donahue, T.M., J.H. Hoffman and R.R. Hodges, Jr., 1982, 

"Venus was Wet: A Measurement of the Ratio of D to H," 

Science, 216, pp. 630-633. 

33. McElroy, M.B., M.J. Prather, and M.J. Rodriquez, 1982, 

"Escape of Hydrogen from Venus", Science, 215, pp. 

1614-1615. 

34. Hartle, R.E. and H.A. Taylor, 1983, "Identification of 

Deuterium Ions in the Ionosphere of Venus," Geophysical 

Research Letters, 10, pp. 965-968. 

82
35. Pollack, J.B., O.B. Toon, and R. Boese, 1980, 

"Greenhouse Models of Venus' High Surface Temperature, 

as Constrained by Pioneer Venus Measurements," Journal 

of Geophysical Research, 85(A13), pp. 8223-8231. 

36a. V.I. Moroz, A.P. Ekonomov, B.E. Moshkin, H.E. 

Revercomb, L.A. Sromovsky, J.T. Schofield, D. Spankuch, 

F.W. Taylor and M. Tomasko, 1985, "Solar and Thermal 

Radiation in the Venus Atmosphere," in Venus 

International Reference Atmosphere, ed. A.V. Kliore, 

V.I. Moroz and G.M. seating, Advances in Space 

Research, 5(11), chapter 6. 

36b. G.M. Keating, J.L. Bertaux, S.W. Bougher, T.E. 

Cravens, R.E. Dickension, A.E. Hedin, V.A. 

Krasnopo].sky, A.F. Nagy, J.Y. Nicholson, L.J. Paxton, 

and U. von Zahn, 1985, "Models of Venus Neutral Upper 

Atmosphere Structure and Composition," in Venus 

International Reference Atmosphere, ed. A.V. Kliore, 

V.I. Moroz and G.M. Keating, Advances in Space 

Research, 5(11), chapter 4. 

360. S.J. Bauer, L.M. Brace, H.A. Taylor, T.K. Breus, A.J. 

liore, W.C. Knudsen, A.F. Nagy, C.T. Russell and 

N.A. Savich, 1985, "The Venus Ionosphere," in Venus 

International Reference Atmosphere, ed. A.V. Kliore, 

V.I. Moroz and G.M. Keating, Advances in Space 

Research, 5(11), chapter 7. 

37. Pollack, J.B., 1981, "Atmospheres of Terrestrial 

Planets," in The New Solar System, ed. J.K. Beatty, B. 

O'Leary, and A. Chaikin, Sky Publishing Corp., 

Cambridge Mass., pp. 57-70. 

38. "Venus Atmospheric Circulation Described by Pioneer," 

1981, NASA Activities, 12(9), P. 10. 

39. "Balloons Over Venus", 1986, Scientific American, 

254(5), p. 69. 

40. "Venus Volcanism: Another Hint," 1989, Science News, 

136(24), p. 383. 

41. Schubert, G. and C. Covey, 1981, "The Atmosphere of 

Venus," Scientific American, 245(1), pp. 66-74. 

42. Prinn, R . G., 1985, "The Volcanoes and Clouds of Venus", 

Scientific American, 252(3), pp. 46-53.

83 
43. Knollenberg, R., L. Travis, M. Tomasko, P. Smith, B. 

Ragent, L. Esposito, D. MoCleese, J. Martonchik, and R. 

Beer, 1980, "The Clouds of Venus: A Synthesis Report," 

Journal of Geophysical Research, 85(A13), pp. 8059-8081. 

44. Woo, R., J.W. Armstrong and A. Ishimaru, 1980, "Radio 

Occultation Measurements of Turbulence in the Venus 

Atmosphere by Pioneer Venus," Journal of Geophysical 

Research, 85(A13), pp. 8031-8038. 

45. Eed.in, A.E., E.B. Niemann, W.T. Kasprzak and A. Seiff, 

1983, "Global Empirical Model of the Venus Thermosphere, 

so Journal of Geophysical Research, 88(A1), pp. 73-83. 

"Correction to 'Global Empirical Model of the Venus 

Thermosphere' by A.E. Hedin et al.," 1983, Journal of 

Geophysical Research, 88(A8), pp. 6352. 

48. Niemann, H.B., W.T. Kasprzak, A.E. Hedin, D.M. Hunten, 

and N.W. Spencer, 1980, "Mass Spectrometric Measurements 

of the Neutral Gas Composition of the Thermosphere and 

Exosphere of Venus," Journal of Geophysical Research, 

85(A13), pp. 7817-7827. 

47. Mengel, J.G., D.R. Stevens-Rayburn, H.G. Mayr and I. 

Harris, 1989, "Non-Linear Three Dimensional Spectral 

Model of the Venusian Thermosphere with Super-Rotation--

II. Temperature, Composition and Winds," Planetary 

Space Science, 37(6), pp. 707-722. 

48. Mayr, E.G., I. Harris, R.E. Hartle, K.H. Schatten, H.A. 

Taylor, K.L. Chan and D.R. Stevens-Rayburn, 1985, 

"Conjecture on Superrotation in Planetary Atmospheres: A 

Diffusion Model with Mixing Length Theory," Advances in 

Space Research, 5(9), pp. 63-68. 

49. Brinton, H.C., H.A. Taylor, H.B. Niemann, E.G. Mayr 

A.F. Nagy, T.E. Cravens and D.F. Strobel, 1980, "Venus 

Nighttime Hydrogen Bulge," Geophysical Research Letters, 

7(11), pp. 865-868. 

50. Paxton, L.J., D.E. Anderson, A.I.F. Stewart, 1985, "The 

Pioneer Venus Ultraviolet Spectrometer Experiment; 

Analysis of Hydrogen Lyman-Alpha Data," Advances in 

Space Research, 5(9), pp. 129-132. 

84
51. Taylor, E.A., H.C. Brinton, S.J. Bauer, R.E. Hartle, 

P.A. Cloutier and R.E. Daniel)., 1980, "Global 

Observations of the Composition and Dynamics of the 

Ionosphere of Venus: Implications for the Solar Wind 

Interaction," Journal of Geophysical Research, 85(A13), 

pp. 7765-7777. 

52. Stewart, A.I.F., J.C. Gerard, D.W. Rusch and S.W. 

Bougher, 1980, "Morphology of the Venus Ultraviolet 

Night Airglow," Journal of Geophysical Research, 

85(A13), pp. 7861-7870. 

53. Bougher, S.W., R.E. Dickinson, E.C. Ridley, R.G. Roble, 

A.F. Nagy, and T.E. Cravens, 1986, "Venus Mesosphere 

and Thermosphere II. Global Circulation, Temperature, 

and Density Variations," Icarus, 68, pp. 284-312. 

54. Kasprzak, W.T., A.E. Hedin, E.G. Mayr, and H.B. Niemann, 

1988, "Wavelike Perturbations Observed in the Neutral 

Thermosphere of Venus," Journal of Geophysical Research, 

93(A10), pp. 11237-11245. 

55. Mayr, E.G., I. Harris, W.T. Kasprzak, N. Dube and F. 

Varosi, 1988, "Gravity waves in the Upper Atmosphere of 

Venus," Journal of Geophysical Research, 93(A10), pp. 

11247-11262. 

56. Hoegy, W.R., L.H. Brace, W.T. Kasprzak and C.T. Russell, 

1990, "Small Scale Plasma, Magnetic and Neutral Density 

Fluctuations in the Nightside Venus Ionosphere," 

accepted for publication in Journal of Geophysical 

Research. 

57. Keating, G.M., F.W. Taylor, J.Y. Nicholson and E.W. 

Hinson, 1979, "Short-Term Cyclic Variations and Diurnal 

Variations of the Venus Upper Atmosphere," Science, 

205(4401), pp. 62-64. 

58. "Magnetic fields in the Ionosphere of Venus", J.G. 

Luhman and T.E. Cravens, to be published in Space 

Science Reviews, 1990. 

59. Phillips, J.L. and D.J. McComas, 1990, "The 

Magnetosheath and Magnetotail of Venus," to be published 

in Space Science Reviews.

85
60. Russell, C. T., E. Chiou, 3. G. Lubmann and L. H. Brace, 

1990, "Solar Cycle Variations in the Neutral Exosphere 

Inferred from the Location of the Venus Bow Shock," 

Advances in Space Research, 10(5), pp. (5)5-(5)9. 

61. Brace, L.B., R.F. Theis and J.D. Mihalov, 1989, "Solar 

Wind and Solar Cycle Control of the Venus Nightside 

Upper Ionosphere," IAGA, Session 2.7/4.11. 

62. Brace, L.H., W.T. Kasprzak, H.A. Taylor, R.F. Theis, 

C.T. Russell, A. Barnes, J.D. Mihalov and D.H. Hunten, 

1987, "The lontail of Venus: Its Configuration and 

Evidence for Ion Escape," Journal of Geophysical 

Research, 92(A1), pp. 15-26. 

63. Knudsen, W.C., A.J. Kliore and R.C. Whitten, 1987, 

"Solar Cycle Changes in the Ionization Sources of the 

Nightside of Venus," Journal of Geophysical Research, 

92(Al2), pp. 13391-13398. 

64. Kliore, A.J., and R. Mullen, 1987, "Solar Cycle 

Influence on the Topside Plasma Scale Height of the 

Venus Dayside Ionosphere," Bulletin of the American 

Astronomióal Society, 19, p. 846. 

65. Lanzerotti, L. 3., and C. Uberoi, 1989, "The Planets' 

Magnetic Environments," Sky and Telescope, 77(2), pp. 

149-152. 

66. Dickenson, R. E., and S. W. Bougher, 1986, "Venus 

Mesosphere and Thermosphere. I. Heat Budget and 

Thermal Structure," Journal of Geophysical Research, 91, 

pp. 70-80. 

67. Bougher, S.W., R.E. Dickenson, E.C. Ridley, R.G. Roble, 

A.F. Nagy and T.E. Cravens, 1986, "Venus Mseosphere and 

Thermosphere. II. Global Circulation, Temperature and 

Density Variations," Icarus, 68, pp. 284-312. 

68. A.E. Hedin, 1987, "MSIS-86 Thermosphere Model," Journal 

of Geophysical Research, 92, pp. 4649-4662. 

69. Brace, L.E. and A.J. Kliore, 1990, "The Structure of the 

Venus Ionosphere," to be published in Space Science 

Reviews.

86
70. Brace, L.H., W.R. Hoegy, R.F. Theis, 1988, "Solar Euv 

Measurements at Venus Based on Photoelectron Emission 

from the Pioneer Venus Langmuir Probe," Journal of 

Geophysical Research, 93, p. 7282. 

71. Hunten, D.M., 1982, "Thermal and Nonthermal Escape 

Mechanisms for Terrestrial Bodies," Planetary Space 

Science, 30(8), pp. 773-783. 

72. Belotserkovskii, O.M., T.K. Breus, A.M. Kryinskii, V.Y. 

Mitnitskii, A.F. Nagy, and T.I. Gombosi, 1987, "The 

Effect of the Hot Oxygen Corona on the Interaction of the 

Solar Wind with Venus," Geophysical Research Letters, 14, 

pp. 503-506.

87
NASA Report Documentation Page 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

NASA TN-100761 

4. Title and Subtitle 5. Report Date 

The Pioneer Venus Orbiter: 11 Years of Data May 1990 

A Laboratory for Atmospheres Seminar Talk

6. Performing Organization Code 

615 

7. Author(s) 8. Performing Organization Report No. 

90B00 109 

W. T. Kasprzak

10. Work Unit No. 

9. Performing Organization Name and Address

11. Contract or Grant No. Laboratory for Atmospheres 

Goddard Space Flight Center 

Greenbelt, MD 20771

13. Type of Report and Period Covered 

12. Sponsoring Agency Name and Address Technical Memorandum 

National Aeronautics and Space Administration

14. Sponsoring Agency Code Washington, D.C. 20546-0001 

15. Supplementary Notes 

16. Abstract 

The Pioneer Venus Orbiter has been in operation since orbit insertion on 

December 4, 1978. For the past 11 years, it has been acquiring data on the 

salient features of the planet, its atmosphere, ionosphere, and interaction 

with the solar wind. The contents of this document are a summary of a few 

of the results of this mission and their contribution to our general understanding of the planet Venus. Although Earth and Venus are often called twin 

planets, they are only superficially similar. Possessing no obvious evidence 

of plate tectonics, lacking water and an intrinsic magnetic field, and having 

• hot, dense carbon dioxide atmosphere with sulfuric acid clouds makes Venus 

• unique object of study by the Orbiter's instruments. 

17. Key Words (Suggested by Author(s)) 18. Distribution Statement 

Venus 

Pioneer Venus Orbiter 

Venus atmosphere, ionosphere Unclassified - Unlimited 

Subject Category 88 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of pages 22. Price 

92 

Unclassified Unclassified

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